Circuit breaker



Sept. 1, 1936. s. s. GRADY 2,052,564

CIRCUIT BREAKER Original Filed April 30, 1931 4 Sheets-Sheet 1 Jay!INVENTOR ATTORN EY Sept. 1, 1936. s, s. GRADY CIRCUI T BREAKER 4Sheets-Sheet 2 Original Filed April 30, 1951 INVENTOR AMI/J61- ATTORN EYSept. 1, 1936. s s GRADY 2,052,564

CIRCUIT BREAKER Original Filed April 30, 1931 4 Sheets-Sheet 3 INVENTORATTORNEY Sept. 1, 1936.

s. s. GRADY 2,052,564

CIVRCUIT BREAKER Original Filed April 30, 1951 4 Sheets-Sheet 4 INVENTORATTORNEY Patented Sept. 1, 1936 CIRCUIT BREAKER Stephen S. Grady.Magnolia, N. 0., assignor to Fusoid Electric 00., Inc

York

., a corporation of New Application April 30, 1931, Serial No. 533,948

' Renewed November 22, 1935 19 Claims. (Cl. 200-48) My present inventionrelates generally to circuit breakers, and has particular reference tocircuit breakers of the type wherein an insulating member, hereinafterreferred to as an interposer, is adapted to be interposed between a pairof complementary contacts when the circuit is to be broken.

A circuit breaker of the type to which my invention relates is usuallycomposed of a suitable housing within which a pair of contact membersare mounted, the contacts being spring-pressed toward each other so asto be normally together. The interposer is usually mounted for slidablemovement, a spring urging it into an operative position between thecontacts and a releasable latch serving to hold it in a normallyretracted and poised position. A control handle may be manipulated toset the interposer into its latched position, and a trip mechanism isprovided for releasing the latch whenever the circuit is to be broken.

A general object of my present invention is to provide an improvedcircuit breaker of this general character, and, more particularly, onewhich is more compact and reliable, less expensive to manufacture, lesscomplicated in structure and operation, and of improved efliciency.

A particular object of my invention is to provide a circuit breakerwhich may be employed in any position, thereby permitting it to be usedunder a wide variety of conditions which different requirements maypresent.

In all circuit breakers of this general type, the objective sought to beaccomplished is tobreak an electric circuit whenever the load in thecircuit exceeds a certain predetermined maximum. Provision must be made,however, for transient or momentary overloads due, for example, toopening and closing the circuit. In accordance with my presentinvention, I provide not only a mechanism, responsive to loadvariations, which serves to operate the trip mechanism directly underpredetermined overloads, but also a normally inoperative auxiliarydevice for taking care of lesser overloads of a sustained character. Theauxiliary device is relatively sluggish in operation and is preferablyin the form of a thermostat. Under certain predetermined overloads, lessthan are necessary to operate the trip mechanism directly, thisthermostatic deiice will operate the-trip mechanism if such overloadsare sustained; but

due to its sluggish character, the thermostat will not operate the tripmechanism under momentary or transient overloads. 7

It is a particular feature ofmy present inveneration of any undesiredheat.

tion to provide an arrangement whereby the thermostat is normallyshort-circuited and therefore totally inoperative. Although thermostatshave been employed in circuit breakers in the past, I am not aware ofany prior arrangement which does not require current to be constantlyflowing through the thermostat. By avoiding this, I am enabled toprovide a device which is more easily set or adjusted to predeterminedloads, and which operates for long periods of time without gen-Furthermore, the operation of my device involves no losses due tovoltage drop across the thermostat, or deterioration of the thermostatdue to overheating; and my present circuit breaker operates eflicientlyand in a predetermined manner regardless of external temperatureconditions,

A further feature of my invention lies in providing an improvedmechanism for setting the interposer. In accordance with my presentinvention, an extremely simple and compact mechanical arrangementprevents the interposer from being controllably moved or adjusted exceptwhen the contacts are separated. Any unwarranted or deliberate attempt,therefore, to hold the interposer out of operative position is whollyunsuccessful, and my present device is therefore entirely foolproof,resisting and preventing any purposeful attempts to render the circuitbreake inoperative and thereby permitting passage of t e.

very.overloads which the circuit breaker is designed to prevent.

I achieve the foregoing objects and advantages, and such other objectsand advantages as may hereinafter appear or be pointed out, in themanner illustratively exemplified in the accompanying drawings, wherein-Figure 1 isa cross-sectional elevation through a circuit breaker of thepresent character, this view being taken substantially along the line liof Figure 2;

Figure 2 is a plan view of Figure 1 with the cover removed and withcertain parts omitted or sectioned for the sake of clearness;

Figure 3 is a cross-sectional view taken substantially along the line3-3 of Figure 1;

Figure 4 is a. view similar to Figure 1. showing the circuit breaker inits normal inoperative position, 1

Figure 5 is a cross-sectional view taken substantially along the line5--5 of Figure 4;

Figure 6 is a cross-sectional view taken substantially along the line6--6 of Figure 4;

Figure 6A is a; perspective view of one of the structural elements:

Figure 6B is a perspective view of the interposer;

Figure 7 is a perspective view of certain portions of the tripmechanism;

Figure 8 is an enlarged fragmentary view taken in the direction ofFigure 4;

Figure 9 is a plan view of Figure 8;

Figure 10 is a view similar to Figure 8 showing the parts in therelationship they assume after the interposer is set into poisedposition;

Figure 11 is a plan view of Figure 10 with the parts in the full-linepositions of Figure 10;

Figure 12 is a plan view of Figure 10 with the parts in the dot-and-dashpositions of Figure 10;

Figure 13 is a fragmentary cross-section along the line I3l3 of Figure11;

Figure 14 is a similar view taken substantially along the line |4--l4 ofFigure 12; and

Figure 15 is a diagrammatic view showing the electrical connections.

The housing of my present circuit breaker consists, in general, of twoparts, a bottom part or container 20 and a top part or cover 2i. Thesetwo elements are provided-with recesses, openings, depressions,shoulders, and the like to accommodate the several parts which will behereinafter described in greater detail. The cover is held in positionby means of the studs 22 and 23, and the entire circuit breaker isadapted to be mounted upon a panel board or the like by studs or thelike which are adapted to pass through the bores 24 and 25 provided forthis purpose.

The contact member 26 is secured as at 21 to the housing and is adaptedto cooperate with the complementary contact member 28 mounted within thehousing. The member 28 is carried upon a stem 29 of copper or the like,and is constantly engaged by a leaf spring 30 which tends to hold thecontacts 26 and 28 together, as shown in Figure 1. It is these contactswhich are to be separated by my present device under certain overloadconditions.

The separation of the contacts is accomplished by means of theinterposer 3| which is shown in retracted poised position in Figure 1,and in forwardly projected operative position in Figure 4. A pair ofcoiled compression springs 32 constantly urge the interposer forwardlyinto the position of Figure 4, wherein it will be noted that thecontacts 26 and 28 are held in separated position.

A latch arrangement, presently to be described,

serves to hold the interposed in its retracted position, against theaction of the springs 32, whenever the circuit breaker is in use; andthe trip mechanism and manner of operation thereof for releasing thelatch and permitting the springs 32 to function will be hereinafterdescribed in greater detail.

The interposer by itself is shown most clearly in Figure 63. It issubstantially flat, having a wedge-shaped forward edge 33 and tworearwardly disposed ears 34 adapted to engage with the forward ends ofthe springs 32 respectively. A longitudinal slot 35 has a forwardtransversely enlarged portion 33 which defines the shoulder 37. By meansof a separate metallic member 38 riveted in position as at 39, adownwardly projecting shoulder 48 is provided behind the shoulder 31.

Before describing the other mechanism, I will point out that. in settingthe interposer into its retracted position, a tongue engages theshoulder 37 to force the interposer rearwardly. After a predeterminedrearward movement, the shoulder 40 engages a complementary relativelyfixed shoulder and thereby latches the interposer in rearward position.When the latch is released, the interposer must be free to advanceforwardly under the action of the springs 32, and, in accordance with mypresent invention, it is impossible to prevent these springs fromoperating once the interposer has been set. This is accomplished by anarrangement whereby the tongue for engaging the shoulder 31 isexcluded-from the enlarged space in front of the shoulder 37 at alltimes except when the contacts 26 and 28 are separated. As soon as thecontacts 26 and 28 are closed, the interposer is rendered trip free,which means that the control tongue is forced laterally away from infront of the shoulder 31, and, more particularly, into the longitudinalslot 35.

The'interposer 3| rests slidably upon the base 4| of the housing 28, andthis baseis provided with the two longitudinal channels 42 which areadapted to accommodate the springs 32 when the parts are assembled.Within a depression 43', the latching and trip mechanism are arranged,this portion of my device being most clearly illustrated in Figure 7 andin the succeeding figures.

Referring to Figure '7, and also to Figures 8 and 10, I will point outthat the member with which the projection 40 engages, in order to latchthe interposer, is in the form of a strip of metal 43 whose rear edge iscentrally cut out to provide a shoulder 44 which positions itselfdirectly in front of the projection 40 when the interposer is latched.

At its forward end, the strip 43 curves downwardly as at 45, andimmediately behind this portion a downward tab 46 is struck out of thematerial, leaving an opening 41.

At its rear edge, the strip 43 is bent downwardly and then rearwardly toprovide the tab 48. Pressure downwardly upon the tab 48 withdraws theshoulder 44 from in front of the projection 40 and thereby releases thelatch. I

Riveted to the under-surface of the strip 43 is the forward end of aU-shaped bimetallic thermostat, the two arms 49 and 50 of which areprovided at their rear ends with the openings 5| and 52 respectively.Insulating strips 53 are arranged on opposite sides of the forward endof the thermostat as'shown most clearly in Figure 8, since the strip 43forms no part of the operative electric circuit. I

Underneath the arms 49 and 50 are the conductive strips 54 and 55,respectively, attached at their rear ends to the rear ends of the arms49 and 50. The thermostat is normally shortcircuited by a copper bridge56 which engages the under-surfaces of the strips 54 and 55 under normalconditions.

The bridge 56 is carried upon the arm 51 of a bell crank whose other arm58 extends vertically and is provided with the pivot pins 59. Theforward end of the arm 51 is arranged over the tab 48, so that when thearm 51 moves downwardly this forward end encounters the tab 48.

Under normal conditions, the bell crank is in the position of Figure 1,a spring 60 hearing upwardly against the arm 57. It will be noted thatelectric circuit hereinafter to be described. It the arm 58 is movedforward no further than this, any sustained minor overload will causethe thermostat to flex downwardly, carrying the strip 43 with it andreleasing the latch. Momentary or transient minor overloads will nottrip the latch. On the other hand, if the arm 58 is moved forwardly by agreater amount than illustrated in Figure 7, the latch will be trippedimmediately and directly by virtue of the downward pressure of the arm51 upon the tab 48.

Regardless of the manner in which the latch is tripped, it will beunderstood that as soon as the interposer has broken the circuit whichcontrols the movements of the arm 58, the spring 60 will immediatelyrestore the thermostat and its associated parts to the relationship ofFigure 1. l

The pivots 59 are journaled in the U-shaped bearing 6| which is mountedin the housing 20 by means of the stud 62.

The upper end of the arm 58 is engaged by one of the laminations of thecore 93 of the solenoid 64, as shown most clearly in Figures 1 and 4. Itis the energizati'on of this solenoid to lesser or greater degrees whichcontrols the corresponding movements, hereinbefore described of the arm58.

A spring 65 normally urges the core 63 outwardly, i. e., toward theright as shown in the figures; and in its normal position, this core isengaged by a detent 66 as shown in Figure 1. This detent consists of acantilever strip mounted, as at 61, to the housing and adjustable to anaccurate degree by the adjustment screw 68. If the screw 68 is adjusted,the detent 66 engages the core with greater or less force,

- thereby requiring a correspondingly greater or less current to drawthe core 63 into the solenoid.

It is the adjustment of the screw 68 which predetermines the loads underwhich the circuit breaker will operate. For example, the screw 58 may beaccurately adjusted so that a load of, say, 18 amperes is necessary tomove the core 63. .If this adjustment is made, then any currents lessthan this amount will leave the device in the normal condition of Figure1, the thermostat being short-circuited and the interposer beinglatched. The solenoid may be so designed that currents between, say, 18amperes and about 135 amperes will be suflicient only to move the arm 58into the position-of Figure 7; whereas currents greater than 135 ampereswill move the arm 58 by a greater degree. With a structural design ofthis illustrative character, currents between 18 and 135 amperes willnot trip the latch if momentary, but will trip the latch if sustainedbeyond a transient degree. And, in any event, currents greater than 135amperes will cause an immediate release of the latch by the directoperation of. the arm 51 upon the tab 48.

Arranged over the interposer 3! is the cover plate 69 which isillustrated most clearly in Figure 6A. It is substantially H-shaped, thecross portion 10 being slightly depressed and provided with the twoapertures 1|. Upon the depressed portion 10, the rear ends of thecontact strip 29 and the leaf spring 30 rest, being secured in positionby means of the screws 12. The springs 32 are accommodated beneaththe-parallel side arms One of the arms of the plate 69 is bentdownwardly, as at 16, and is connected to the rear of the thermostat arm49 by means of the stud 11 which engages through the opening 5|. Thisstud also holds the arm 49 securely to the housing 20 as shown in Figure5; and a similar stud 18 passes through the opening 52 in the thermostatarm 50 and secures this arm to the housing 20.

The electrical circuit may now be traced with the aid of Figure 15, fromthe contact 26 through the contact 28 and the conductive strip 29 to thecover plate 69, thence through the portion 16 to the thermostat arm 49.When the thermostat is short-circuited, the circuit continues throughthe strip 54 across the bridge 56 to the strip 55 and thence directly tothe stud 18. When the thermostat is operative, the circuit must betraced through the thermostat itself to the stud 18. From the latterstud, an electrical connection (not shown, except in Figure 15) extends,as at 19, to one end of the coil of the solenoid 64, and the other endof the solenoid is connected by a lead to the binding post 8 I, andthence through the strip 82 to the terminal 83. The main outer circuitconnects with the contact 26 and also with the terminal 83.

The strip 82 is attached to the housing by means of the stud 84, asshown most clearly in Figure 1.

The manner in which the interposer 3| is set is most clearly illustratedin Figures 8-14. A control handle projects through the top wall. 2| andis pivoted, as at 9!, in the opposite side walls of the housing topermit the handle to be swung between the positions of Figures 1 and 4.Pivoted to the"handle 90 within the housing, as at the pivot 92, is atongue 93 which is adapted to pivot in a transverse direction, i. e.,from the position shown in Figures 6 and 13 to the position shown inFigure 14. A small, relatively weak spring 94 is associated with thepivot 92 and engages the tongue 93 to urge the latter normally into theposition of Figures 6 and 13.

The leaf spring 39 and also the contact strip 29 are provided with theopenings 95 and 96, respectively, through which the tongue 93 projects,and the extreme lower end of the tongue extends through the slot in theinterposer, either through the slot portion 35 or the enlarged portion36, depending upon the lateral position of the tongue. I

The tongue 93 is provided with the projection or abutment 91 which isshown most clearly in Figures 13 and 14. I Assuming that the parts ofthe device are in the normally inoperative relationship of Figures 4, 8,and 9, it will be observed that the spring 94 is holding the tongue 93in front of the interposer shoulder 31, this disposition of the tongue93 being permitted by virtue of the fact that the contacts 26 and 28 areseparated, whereby the abutment 91 may position itself beneath the leafspring 30, as shown in Figure 13. When the handle 99 is'pushed into theposition of. Figure 1, the tongue 93 engages the interposer shoulder 31and forces the interposer rearwardly, but; at the same time, theabutment 91 bears against the under-surface of the leaf spring 39 andtends to hold the latter in a raised condition. The

withdrawal of the interposer from the position b of Figure 8 into thatof Figure 10 leaves the leaf spring 30 free to push the contact 28downwardly from the full-line position of Figure 10 to the dot-and-dashposition. It is impeded, however, by the abutment 91,and as long asthere is frictional engagement between the tongue 93 and the shoulder31, the tendency of the spring 30 to cam the abutment 91 laterally outof its way is insuificient to accomplish this deflection. As a result,merely swinging the handle 90 into the position of Figure 1 does notclose the contacts 26 and 28, and as long as pressure is exerted uponthe handle 90 the parts remain in the intermediate relationshipillustrated in full-lines in Figure l0 and also illustrated in Figures11 and 13. The moment pressure upon the handle 90 is released, however,the frictional engagement between the tongue 93 and the shoulder 31becomes insufiicient to Withstand the tendency of the spring 30,whereupon the latter snaps down wardly into the dot-and-dash position ofFigure 10 (illustrated also in Figures 12 and 14), and in doing sodeflects the tongue 93 into the position of Figures 12 and 14. In thisposition, it is observed that the tongue is no longer in front of theinterposer shoulder 31 but is disposed within the slot portion 35. Theinterposer is thus rendered trip free the instant that contact isestablished between the contacts 26 and 28.

During the movement of the tongue 93 from the position of. Figure 8 tothat of Figure 10, the lower end thereof will have wedged its way overthe forward end of the strip 43, so that when the interposer is set inpoised latched position, the lower end of the tongue 93 is disposedwithin the opening 41. The purpose of this will now be clear, because ifit is desired to operate the circuit breaker by hand, it is merelynecessary to press the handle 90 from the position of Figure 1 towardthe position of Figure 4; and as the tongue rides over the tab 46, itwill deflect the strip 43 downwardly and thereby release the latch andpermit the interposer to snap into its forward operative position. Underthese conditions, the tongue 93 is again free to position itself infront of. the shoulder 31, the abutment 97 again engaging bencath theleaf spring 39. If desired, a

tongue 93 to be deflected out of the path of the interposer, so thatunder overload conditions a release of the latch will permit theinterposer to advance rapidly forwardly and separate the contacts 26 and28. Any attempt to hold the interposer in retracted position, other thanby means of the latch arrangement, will be. unsuccessful, becausealthough the interposer may be held rearwardly as shown in full-lines inFigure 10, the contacts will not close until pressure upon the handle 99is released; and when such pressure 'is released the closing of thecontacts automatically thrusts the tongue 93 out of the path of theinterposer and leaves the latter free to function in its contemplatedmanner under predetermined overloads.

It will be obvious that changes in the details herein described andillustrated for the purpose of explaining the nature of my invention maybe made by those skilled in the art without departing from the spiritand scope of the invention as. expressed in the appended claims. It istherefore intended that these details be interpreted as illustrative,and not in a limiting sense.

Having thus described my invention and illustrated its use, what I claimas new and desire to secure by Letters Patent is- 1. In a circuitbreaker, a pair of contacts, an interposer for separating the contacts,an electric circuit, a trip for normally anchoring said interposer incircuit making position, a normally inoperative and relatively sluggishdevice adapted to operate said trip, and means responsive to loadvariations in said circuit for rendering said device operative undercertain loads and for operating the trip directly under certain greaterloads.

2. In a circuit breaker, an electric circuit including a pair ofcontacts normally in engagement with one another, an interposer forseparating the contacts, and a trip for normally anchoring saidinterposer in circuit making position, said circuit also including anormally inoperative thermostat adapted to operate said trip, saidthermostat being responsive to load variations in said circuit andoperative under certain loads.

3. In a circuit breaker, a pair of contacts, a device for separating thecontacts, an electric circuit, a trip for normally anchoring said devicein circuit making position, a normally inoperative thermostat adapted tooperate said trip, and

means responsive to load variations in said circuit for rendering saidthermostat operative under certain loads and for operating the tripdirectly under certain greater loads.

4. In a circuit breaker, a pair of contacts, an interposer forseparating the contacts, an electric circuit, a trip for normallyanchoring said interposer in circuit making position, a normallyshort-circuited device in said circuit adapted to operate said trip, andmeans responsive to load variations in said circuit for destroying saidshort-circuit and thereby rendering said device operative under certainloads.

5. In a circuit breaker, a pair of contacts, an interposer forseparating the contacts, an electric circuit, a trip for'normallyanchoring said interposer in circuit making position, a device in saidcircuit adapted to operate said trip, a movable member normallyshort-circuiting said device to render it inoperative, and an electromagnetic mechanism responsive to load variations in said circuit for movingsaid short-circuiting member and thereby rendering said device operativeunder certain loads.

6. In a circuit breaker, a pair of contacts, an interposer forseparating'the contacts, an electric circuit, a trip for normallyanchoring said interposer in circuit making position, a normallyshort-circuited thermostat in said circuit adapted to operate said trip,and means responsive to load variations in said circuit for destroyingsaid short-circuit and thereby rendering said thermostat operative undercertain loads.

7. In a circuit breakena pair of contacts, an interposer for separatingvthe contacts, an electric circuit, a trip for normally anchoring saidinterposer in circuit making position, a thermostat in said circuitadapted to operate said trip,

a movable member normally short-circuiting said thermostat to render itinoperative, and an electromagnetic mechanism responsive to loadthermostat operative under certain loads.

8. In a circuit breaker, a pair of contacts, a

a device for separating the contacts, an electric circuit, a trip fornormally anchoring said device in circuit making position, a normallyshortcircuited thermostat in said circuit adapted to operate said trip,-and means responsive to load variations in said circuit for destroyingsaid short-circuit and thereby rendering said thermostat operative undercertain loads and for operating the trip directly under certain greaterloads.

9. In a circuit breaker, a pair of contacts, a device for separating thecontacts, an electric circuit, a trip for normally anchoring said devicein circuit making position, a thermostat in said circuit adapted tooperate said trip, a movable member normally short-circuiting saidthermostat to render it inoperative, and an electromagnetic mechanismresponsive to load variations in said circuit for moving saidshort-circuiting member and thereby rendering said thermostat operativeunder certain loads, said electromagnetic mechanism being adapted tooperate said trip directly under certain greater loads.

10. In a circuit breaker, a pair of contacts, an interposer forseparating the contacts, an electric circuit, a trip for normallyanchoring said interposer in circuit making position, a thermostat insaid circuit adapted to operate said trip, a movable member normallyshort-circuiting said thermostat to render it inoperative, and anelectromagnetic mechanism responsive to load variations in said circuitfor moving said short-circuiting member and thereby rendering saidthermostat operative under certain loads, said mechanism comprising amagnet coil, an armature under the influence of said coil, and a leverations' in said circuit for moving said short-circuiting member andthereby rendering said thermostat operative under certain loads, saidelectromagnetic mechanism being adapted to operate said trip directlyunder certain greater loads;

said mechanism comprising a magnet coil, an

armature under the influence of said coil, and a lever operativelyinterposed between said armature and said short-circuiting member, saidlever being adapted to engage said trip directly after predeterminedmovement of said lever.

12. In a circuit breaker for an electric circuit,

the combination with a pair of contacts in the circuit, of a device forseparating said contacts into circuit breaking position, a tripfor,normally anchoring said device in circuit making position where saidcontacts engage one another, 8. normally inoperative and relativelysluggish device operatively associated to operate said trip, and amechanism responsive to load variations in said circuit for renderingsaid sluggish device operative upon partial actuation under lightoverloads and for operating said trip directly upon more pronouncedactuation under heavy overloads.

13. In a circuit breaker for 'an electric circuit, the combination witha pair of contacts in the circuit, of a movable interposer, means forurging said interposer to separate said contacts into circuit breakingposition, a trip for normally anchoring said interposer in circuitmaking position where said contacts engage one another, a normallyinoperative and relatively sluggish device operatively associated tooperate said trip, and a mechanism responsive to light overloads in thecircuit for partial actuation to render said device operative in turn toactuate said trip and also responsive to heavy overloads for morepronounced actuation to actuate said trip directly.

14; In a circuit breaker for an electric circuit, a pair of contacts inthe circuit, a movable interposer, springs for urging said interposer toseparate said contacts into circuit breaking position, a trip fornormally anchoring said interposer in circuit making position where saidcontacts engage one another, a normally inoperative and relativelysluggish device operatively associated to operate said trip, and amechanism including a short circuiting member and a lever and beingresponsive to load variationsin said circuit for partially actuatingsaid lever in turn to actuate said short circuiting member to rendersaid sluggish device operative upon light overthe combination with apair of contacts in the circuit, of a device for separating saidcontacts into circuit breaking position, a trip for normally anchoringsaid device in circuit making position where said contacts engage oneanother, a normally inoperative thermostat operatively associated tooperate said trip, and an electromagnetic mechanism responsive to loadvariations in said circuit for rendering said thermostat operative uponpartial actuation under light overloads and for operating said tripdirectly upon more pronounced actuation under heavy overloads.

16. In a circuit breaker for an electric circuit, the combination with'a pair of contacts in the circuit. of a movable interposer, means forurging said interposer to separate said contacts into circuit breakingposition, a .trip for normally anchoring said interposer in circuitmaking position where said contacts engage one another, a normallyinoperative thermostat operatively associated to operate said trip, andan electromagnetic mechanism responsive to light overloads in thecircuit for partial actuation to render said thermostat operative inturn to actuate said trip and also responsive to heavy overloads formore pronounced actuation to actuate saidtrip directly.

17. In a circuit breaker for an electric circuit, a pair of contacts inthe circuit, a movable interposer, springs for urging said interposer toseparate said contacts into circuit breaking position, a trip fornormally anchoring said interposer in circuit'making position where saidcontacts engage one another, a normally inoperative thermostatoperatively associated to operate said trip, and a mechanism including ashort circuiting member and a lever and being responsive to loadvariations in said circuit for partially erative upon light overloadsand for actuating said lever more pronouncedly under heavy overloads tooperate said trip directly.

18. In a circuit breaker, an electric circuit including a pair ofcontacts normally in engagement with one another in circuit makingposition, an interposer for separating the contacts into circuitbreaking position, and a trip, said circuit also including a normallyinoperative thermostat fixed to said trip, said trip normally anchoringsaid interposer in circuit making position, said thermostat beingresponsive to load variations in said circuit and being operative undercertain loads to retract said trip out of interposer anchoring position.

19. In a circuit breaker, an electric circuit including a pair ofcontacts normally in engagement with one another in circuit making posi-10 tion, an interposer, yieldable means for normally to anchor saidinterposer in circuit making 5 position, said thermostat beingresponsive to load variations in said circuit to be thereby deflectedand therewith to deflect said trip to release said interposer.

STEPHEN S. GRADY. 10

